Ligand exchanges and hydroxypalladation reactions of the Wacker process in aqueous solution at high Cl⁻ concentration

Reaction mechanisms and associated free energies of various reaction steps involved in the Wacker process in aqueous acidic conditions at high Cl(-) concentration were investigated using accelerated ab initio molecular dynamics techniques. Several ligand exchange reactions of the catalytic precursor [PdCl(4)](2-) and nucleophilic attack of water at Pd-coordinated ethene (hydroxypalladation) were looked at in great molecular level detail. This work underlines the key role of the trans effect of Pd-coordinated ethene in the structure and dynamics of solvated Pd(II) complexes. Irrespective of Cl or water ligation at the trans position, the hydroxypalladation proceeds through an anti mechanism where an outer-sphere water attacks an ethene carbon atom in an anti fashion. Extensive molecular dynamics simulations were used to analyze various reaction mechanisms and unravel the stereochemistry of the crucial hydroxypalladation step.